Produção de metano através da codigestão anaeróbia de vinhaça e capim-elefante e avaliação do efeito da adição de bicarbonato de sódio como alcalinizante

Abstract

Most of the energy consumed in the world comes from burning fossil fuels, a limited and pollutants emitting source. The growing concern about preserving the environment has stimulated the search for clean energy sources, and within this context biofuels stand out as a promising energy matrix. In order to produce methane, the present study used vinasse and elephant grass juice as substrates for anaerobic digestion in batch reactors maintained at a temperature of 35°C and rotation of 120 rpm. The reactors were composed by different proportions of vinasse and elephant grass juice (vinasse diluted to 50 and 75% (v/v), grass diluted to 50% (v/v) and mixture of vinasse/elephant grass juice (V/EG) of 50/50 (% v/v)), and inoculated with sludge collected from a UASB (Upflow Anaerobic Sludge Blanket) reactor used in sewage treatment. To the reactors containing the 50/50 (% v/v) V/EG ratio, it was added sodium bicarbonate in concentrations of 0.05, 0.10 and 0.25 gNaHCO3.gCOD-1 (Chemical Demand of Oxygen) to evaluate its effect on buffering the reaction medium. The performance of the reactors was analyzed through the volumetric production of methane and the efficiencies of conversion of carbohydrates and removal of COD and total, fixed and volatile solids. It was found that the addition of sodium bicarbonate was efficient in reducing the pH variation of the reactors, and that elephant grass juice was not effective in methane production. The highest specific methane production was 1364.1 mL.gTVS-1 (Total Volatile Solids), obtained by the reactor containing diluted vinasse at 75% (v/v) as substrate. It was observed that bicarbonate favored the generation of methane when added in lower concentrations, with the reactor to which 0.05 gNaHCO3.gCOD-1 was added producing 836.18 mL.gTVS-1.